One common method for troubleshooting computers in the field is simply to remove suspected faulty components and to replace them with known good ones. Removed components are often then returned to the manufacturer for testing and repair. As it happens, the majority of power supply units returned in this manner are found by the manufacturers to be operating correctly upon receipt. In such cases, the power supply unit should not have been removed and replaced. It would be desirable, therefore, to provide a means by which a computer power supply can be tested for proper operation conveniently in the field.